When fabricating semiconductor devices, silicide, which is a compound of metal and silicon, is often included for electrical contact between a gate electrode, source/drain, and metal lines.
Cobalt silicide, which is a compound of cobalt and polysilicon, is often used for a semiconductor device fabricated in 0.18 μm or smaller technology. However, the resistance of the cobalt silicide rapidly increases as the width of a gate poly decreases to less than 65 nm. To overcome this limitation, nickel silicide, formed using nickel (Ni), can be used since it is less influenced by the width of the gate poly.
However, since Ni layers are typically deposited using physical vapor deposition (PVD), it makes it difficult to properly deposit the layers on narrow active regions (source/drain regions) between gates. Atomic layer deposition (ALD), which is a process of depositing a layer at an atomic level to reduce residual impurities in the layer, has been studied recently as a possible solution. In ALD, a Ni layer is formed through thermal decomposition at high temperature using Ni—CxHy. This Ni layer contains a large amount of carbon impurities, which increases the resistance when nickel silicide is formed.